Update cities.txt

Added Porto Alegre, Brazil.
Corrected shrunked Vienna bbox
Pretty-printed cities.json output
Merge pull request #54 from ftrebien/master

Added Porto Alegre, Brazil
Fixed Porto Alegre spaces/tabs and added to downstream files
Merge branch 'master' of git://github.com/NelsonMinar/Extractotron
Moved cities.json inline with index.html
Removed separate cities.json
Cleaned up part of bbmap.js that was unused